Selective alkane co-inclusion by methylene- and adamantane-bridged macrocycle with biphenyl units

A methylene- and adamantane-bridged macrocycle with four biphenyl units (1) was synthesized as a host molecule. The vapor diffusion of n-hexane into a chloroform solution of 1 afforded a co-inclusion crystal (1a) containing both guests, which was confirmed by X-ray crystallographic analysis. In the case of the other four hexane isomers, a crystal (1b) containing only one chloroform molecule was obtained, indicating the selective inclusion of n-hexane from among the five hexane isomers. When n-heptane or n-pentane instead of n-hexane was employed as an alkane guest, crystal 1b or guest-free crystal 1c was formed, showing that the macrocycle recognizes the length of the alkyl chain. Furthermore, when dichloromethane was used instead of chloroform, crystal 1d with only a dichloromethane guest was generated, showing that chloroform is essential for the accommodation of n-hexane into the crystals.